Shock absorber and suspension mechanism

ABSTRACT

This invention relates to a vibration damping mechanism adapted for use as shock absorber and suspension strut advantageously used on automotive and railroad vehicles. The mechanism comprises a cylinder mechanically connected with axle-mounting means with a piston slidably mounted in the cylinder. The piston divides the interior space of the cylinder into first and second chambers. The piston is connected rigidly with a piston rod, a substantial portion of which is hollow. The interior space of the hollow piston rod includes an upper high pressure gas chamber and a lower liquid space which is fluidically connected with said second chamber. The main improvement resides in the provision of a fluid flowlimiting communication means connected and adapted for returning occasionally accumulated gas from the chamber back into the said gas chamber.

United States Patent 1191 Katsumori et a1.

14 1 Apr. 16, 1974 SHOCK ABSORBER AND SUSPENSION MECHANISM [75]Inventors: Teiji Katsumori; Yoshisuke Ohsaka,

both of Yokohama; vTetuo Kato, Kawasaki, all of Japan [73] AssigneesTokico Ltd., Kawasaki-shi,

Kanagawa-ken, Japan 221 Filed: Dec.29, 1971 [21] Appl. No.: 213,329

[30] Foreign Application Priority Data Dec. 29, 1970 Japan 45-126612Apr. 19, 1971 Japan 46-25143 [52] US. Cl 188/314, 188/269, 188/286,188/317, 267/DIG. l, 267/64 R [51] Int. Cl. F16d 9/06, F16d 9/32 [58]Field of Search 188/269, 282, 314, 317, 188/284, 286, 316; 267/64 R,DIG. l

[56] References Cited UNITED STATES PATENTS 2/1931 Lewis 188/269 4/1965Loewis 188/269 9/1969 Hoffmann et a1... 188/269 4/1932 Messier 188/269Whisler, Jr. et a1. 188/282 Watson 188/284 Primary Examiner-George E. A.l-lalvosa Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn &Macpeak [5 7] ABSTRACT This invention relates to a vibration dampingmechanism adapted for use as shock absorber and suspension strutadvantageously used on automotive and railroad vehicles.

The mechanism comprises a cylinder mechanically connected withaxle-mounting means with a piston slidably mounted in the cylinder. Thepiston divides the interior space of the cylinder into first and secondchambers. The piston is connected rigidly with a piston rod, asubstantial portion of which is hollow. The interior space of the hollowpiston rod includes an upper high pressure gas chamber and a lowerliquid space which is fluidically connected with said second chamber.

The main improvement resides in the provision of a fluid flow-limitingcommunication means connected and adapted for returning occasionallyaccumulated gas from the chamber back into the said gas chamber.

1 Claim, 12 Drawing Figures MTENTED APR 16 I974 SHEET 1 OF 3 SHOCKABSORBER AND SUSPENSION MECHANISM This invention relates to a vibrationdamping mechanism adapted for use as shock absorber and suspension strutadvantageously used on automotive and railway vehicles.

The main object is to provide a vibration damper mechanism of the abovekind and operable in the joint hydraulic and'pneumatic mode wherein ahigh pressure gas is sealed in the mechanism and special caution is paidfor the prevention of leakage of the sealed-in gas or air from inside tooutside of the mechanism.

A further object is to provide an efficient vibration damper mechanismhaving a stabilized damping performance and an efficient heatdissipation performance.

These and further objects, features and advantages will become moreapparent when read the following detailed description of the inventionby reference to the accompanying drawings.

FIG. 1 is an axial section of a first or main embodiment of theinvention.

FIG. 1A and FIG. 1B are enlarged parts of the first embodiment shownin-FIG. 1.

FIG. 2 is an enlarged sectional and detail view of the uppermost part ofthe first embodiment, when, however, it is fitted with a gas or oilintroducing or discharging valve system. I

FIGS. 3, 4 and 5 represent similar view to FIG. 1, showing, however,respective modifications from the first embodiment.

FIG. 5A is a part of FIG. 5 expressed on a larger scale.

FIG. 6 is a similar view to FIG. 1, showing a further modification.

FIG. 6A is an enlarged part and detail view of FIG. 6

' FIGS. 7 and 8 are similar views to FIG. 1, showing further twomodifications therefrom.

Referring now to the accompanying drawings, several preferredembodiments of the invention willbe described hereinafter in detail.

In FIG. 1, numeral -1 represents an upright cylinder containing oil orthe like incompressible liquid within the interior space thereof, aswill be more specifically described.

A piston 2 is sealingly and slidably received in the cylinder 1 anddefines the interior space thereof into an upper pressure chamber A" anda lower pressure chamber B, the cylinder being open at its top end andclosed at its bottom end 1a.

A piston rod 3', only partially shown, has a hollow part at its lowerend which extends into the interior space of cylinder I and is fixedlyattached at its lowermost extremity to the piston 2 by screw connectionat 100.

A dust seal 4 is made from a resilient material, such as soft rubber,plastics or the like, attached with a metal ring 8, and inserted at thetop end of cylinder 1 between the latter and the hollow rod part 3a andkept in position by its own elasticity, for preventing invasion offoreign matters from outside into the interior space of the cylinder.

Numeral 5 represents a sealing packing made from soft rubber or the likematerial and kept sealingly in position directly below the dust seal 4and between the cylinder 1 and the hollow rod part 3a, for preventingleakage of the oil from the interior space of the cylinder 1 towardsoutside. Directly below the sealing packing 5, there is provided a guidering 6 positioned between the cylinder 1 and'the hollow rod part 3a foreffectively guiding the sliding movement of the rod 3.

For firmly positioning the dust seal 4, there are provided pressurespring clips 101 and 102, as most clearly be seen from FIG. 1A. Forretaining the guide ring 6, there is provided a spring clip 9, as mostclearly seen therefrom.

Guide ring 6 is recessed to form a ring space 7 which is kept in fluidcommunication through a fine gap provided between tye hollow rod part 3aand the guide ring 6 with the pressure chamber A defined by the memhersI, 2, 3 and 6 and filled with oil. It will thus be seen from theforegoing that the assembly consisting substantially of the members 4,5, 6 and 8 provides an effective sealing and guide means at the top openend of the cylinder 1 and for the slidable hollow rof part 3a.

The interior space of the hollow rod is divided into a lower oil chamberC and an upper gas chamber D, as seen. The gas pressure contained in thechamber D may attain 30 35 kgs/sq. cm as an example.

Piston 2 is formed a plurality of axia passage openings 10 which allowfree fluid communication between both liquid chambers A" and B.

The piston 2 is further formed with at least an axial oil passageopening 11 for allowing, when necessary, fluid communication betweenchambers C" and Each of these passage openings 11, only one thereof isseen, is enlarged at its intermediate portion between the bothextremities thereof, so as to provide a valve chamber 113 in which acheck valve 12 and a valve spring 13 are provided for allowing onlyunidirectional oil flow from the upper oil chamber C to the lower B. Aplurality of similar passage openings 14, only one thereof being seen,are formed axially through the piston 2, a valve chamber 116 beingformed in the similar way between the upper and lower extremities ofeach of these passage openings 14. The valve chamber 1 16 contains acheck valve 15 and a valve spring 16 for allowing unidirectional oilflow reversedly from the lower B to the upper oil chamber C.

The valve assembly comprising passage opening 11, check valve 12 and itsspring 13 acts as first damping force-generating means during upwardsmovement of piston 2 in the case of the telescopic expansion stroke ofthe whole damper assembly by providing substantial resistant or dampingforce to the oil flow from chamber C" to chamber B. In the similar way,the valve assembly comprising passage opening 14, check valve 15 and itsspring 16 acts as a second clamping forcegenerating means duringdownward movement of piston 2 in the case of the telescopic collapsingstroke of the whole damper assembly by providing substantial resistantor damping force'to the flow in the reversed sense.

Although in the foregoing, specifically selected check valve typedamping means have been shown and described, a corresponding number offlow reducing orifice means can be replaced therefor. As a furtheralternative, check valve means or the like flow reducing or checkingmeans can be provided between the chambers A and C in place of thoseprovided between the chambers B and C.

At an intermediate position between the upper and lower ends of thehollow rod part 3a and on the outer peripheral surface thereof, there isprovided a circular flange piece 17 fixedly mounted by welding or thelike conventional fixing measure and serving as a stop means when therod 3 has arrived at its allowable uppermost axpanded position and bybringing its upper surface 17a into abutment with the lower surface 6aof the guide ring 6.

Numeral 18 represents a communication tube contained in the commoninterior space of the hollow rod part 3a and the piston 2. The upper endextremity 18b of this tube 18 passes fixedly through the wall of thehollow rod at a slight higher level than the ring flange 17 and opens tothe ring-shaped pressure chamber A, while the lower end extremity 18b ofsaid tube 18 opens at the chamber C. Thus,'it-will be seen that thespecial position of'the upper tube opening 18b varies with movement ofthe piston rod assembly 2; 3. Therefore, it will be further seen thatsaid upper opening 18b may be brought into fluid communication with theuppermost part of the chamber A or even with the ring space 7communicating therewith when the piston-rod assembly occupies its upperstroke end.

The lowermost opening 1800f said communication tube 18 may be modified,so far as its bore 18a connects with the central liquid chamber C orwith the lower oil chamber B.

Numeral 19 represents an elongated cup-shaped cover which is fixedlyattached to the closed upper end of the hollow rod part 3a and acushioning member 20 is attached fixedly to the reduced and rigidextension 3b of the said part 3a. It will thus be seen that the rod 3consists substantially of the both parts 3a and-3b. For 'fixinglyattaching the cushioning member 20, consisting of two mating parts 20aand 20b as shown, there are provided a washer .21 and nut 22 which hasbeen threaded tightly'on the upper male threaded part of the rodextension 3b. Numeral 23 'represents a part of the vehicle chassis andresiliently squeezed by and between the cushoning members 20a and 20bfor mounting-the piston-rod assembly.. Ring 6 is held in position byspring clip 9'. l i

The bottom closed end la of the cylinder 1 is attached fixedly with anattaching member 24, preferably made into a ring as shown, by welding orthe like conventional fixing means. This attaching member 24 is attachedfixedly to an axle-mounting means, not shown.

The whole assembly so far shown and described may be utilized as a shockabsorber or vehicle suspension, as the case may be.

Next, the operation of the shock absorber or vehicle suspension havingthe foregoing structure will be described hereinbelow in detail.

When the vehicle is in its stationary positiomthe piston 2 is positionedat a neutral or an intermediate position within the interior of thecylinder 1. In this way, the whole mechanism will support'the allocatedweight of the chassis. This bearing load can be naturally reduced, whenthe mechanism is provided with a mechanical or pneumatic suspensionspring, not shown, attached thereto.

By the gas pressure exerted by the contained high pressure gas or air inthe central chamber D, the piston-rod assembly 2; 3 will be urged tomove upwardly with a certain upwardly directing force, as shown in asimplified and schematic way by an arrow W for supporting the allocatedchassis weight.

. Now, it is assumed that the piston 2 is positioned at its neutralposition and the gas pressure in the gas chamber D" at this stage be atP, the said expandingly urging force Wmay be calculated by the followingformulae (1) and (2):

where,

V stands for the gas volume contained in chamber D" when the piston hasbeen extended to a maximum stroke position; P stands for thecorresponding gas pressure; S stands for the maximum deformationdistance as measured from said maximum stroke position to the neutralone; d stands for the outer'diameter of the hollow piston rod part 3a.

As was above referred to, the allocated chassis load is born by thisexpandingly urging force W.

As commonly known, it is desired to maintain the height of the chassisfrom the ground surface ata constant level as possible, irrespective ofincrease or decrease in the chassis side load. With use of the mechanismaccording to this invention, the desired constant height of the chassiscan be substantially satisfied by varying said expandingly urging forceW. This feature willbe described more in detail hereinbelow.

It is further assumed that when the vehicle is held in itsstationarystate and the chassis side'load or weight is increased by anincrement W and the gas pressure in chamber D""isincreased by P,, thenP, [Wei/0dr] Under these conditions, the chassis side weight increment Wis supported-by the increased pressure increment P thus the chassisheight with the vehicle held at its stationary position will notbesubject to alteration.

On the contrary, when the chassis side weight is reduced by W with thevehicle kept in its stationary position, and the gas pressure prevailingin the chamber D" is reduced by P which is calculated by the followingformula the chassis height of the vehicle held stationary will besubject no alteration.

in FIG. 2, an embodiment of an apparatus adapted for adjustment of thechassis height by modification of the gas pressure in the chamber D" isshown only schematically.

In FIG. 2, numeral'33 represents a gas pressure adjusting duct which hasbeen bored axially and centrally through the rod extension 3b and 34 and35 represent two mutually and mechanically coupled valve body elementsto form a body assembly which is bored axially with a fluid passage 36adapted for introducing gas or oil into the said chamber D through saidduct 33. The valve body assembly 34; 35 is firmly held in position bythe threaded engagement at 105. The duct 33 is sealed off towardsoutside by the provision of a sealing packing 35a which is held inposition, as shown, on the outer periphery of the lower hollow valvebody element 35 and against a shoulder 106 formed on the axial bore wallof rod extension 3b. Numeral 37 represents a valve stem which is fixedlyattached at its bottom end with a valve disc 38 carry fixedly aresilient sealing member 38a, the latter normally sealing off the valveseat 35b formed at the lower end of lower valve body element 35.

The valve stem 37 can move axially of the fluid passage 36 and the upperend of said stern protrudes out of the interior of upper valve bodyelement 34. A compression spring 39 is provided and tensioned betweenlower valve body element 35 and a stop member 37a attached to said stem37 so that the valve disc 38, together with sealing member 38a, is heldresiliently and normally at the valve closing position as shown, so asto shut off the passage 36 thereat.

A pressure hose fitting of conventional design and being provided with amanually operable pusher is attached sealingly to the upper threaded endof the rod extension 3b. By manually operating pusher so as to collideagainst the enlarged head of valve stem 37 which is thus depresseddownwards for introducing high pressure gas flow, from a certain gas orair reservoir at a pressure of about'4O kg/sq. cm by way of example. Bythis operation, valve disc 38, together with sealing member 38a, willrecede downward from contact with valve seat 35b so that the introducedhigh pressure gas flow will be led through the duct 33 into the gaschamber D for increasing the pressure prevailing therein.

Or alternatively, when it is desired to reduce the gas pressureprevailing in the chamber D," the gas or air reservoir, not shown, isdetached from the other end of said supply hose and then the pusher, notshown, is manipulated to open again the valve at 38; 38a relative to theseat 35b. The gas flow will thus be reversed in its direction andtherefore, desired quantity of pressure gas may be discharged from thegas chamber D.

When occasion may demand, oil may be introduced to the oil chamber C"via the gas chamber D substantially by flowing after the aboveprocedure. When discharging oil from the interior of the shock absorberto a desired degree, the absorber maybe positioned at an invertedposition.

By adopting any one of the above procedures, the W-S characteristiccurve of the shock absorber can be modified as desired. Naturally, Sdenotes the strain.

When the vehicle is running and the chassis oscillates up and down, theshock absorber will be subjected once to the expanding vibratinginfluence. In this case, the piston 2 will elevate within the cylinder 1so that oil in the chamber C is discharged therefrom through the bore18a of communication tube 18 into the chamber A and through passagebores 11 into the chamber B upon forcibly opening valves 12 against theaction of respective valve springs 13 and escape through these reducedflow passages 11 thus opened, into the pressure oil chamber B. The thusgenerated flow resistance force will act as vibration damping force sothat the vibration energy of the vehicle is damped. In this case, theoil quantity corresponding to the reduced or displaced volume caused bythe receding movement of the piston rod 3 from within the interior spaceof the cylinder 1 will be supplemented by the oil flowing fromthechamber C into the chambers A and B. In this case, the effectivevolume of the chamber D will be subject to a corresponding expansion andthe gas pressure prevailing therein will be lowered correspondingly.

On the contrary, when the shock absorber will be subject to a collapsingeffect by the reversed vibrating movement of the vehicle, piston 2 willdescend in the cylinder 1 and the oil prevailing in the chamber A" willbe further pressurized and try to escape partially therefrom through thebore 18a of the communication tube 18 into the chamber C, thereby theflow passage 14 being opened by moving the respective check valves 15 intheir opening position against the action of the respective valvesprings 16. This flow restricting action or flow resistance will act asthe damping action so that the vibration energy of the vehicle ispartially absorbed and thus damped. The oil quantity corresponding tothe volume reduced in the cylinder 1 caused by the invading movement ofpiston rod 3 into the interior space of the cylinder 1' is dischargedfrom the chamber B into the chamber C, thus the effective volume of gaschamber D being correspondingly reduced and the gas pressure prevailingtherein will be elevated correspondingly.

The communicating tube 18 will act normally as a kind of dampingforce-generating means for allowing flow-restricting passage of oilresponsive to the reciprocating movement of the piston-rodassembly, andthe further provide the following salient advantage.

More specifically, with the aforementioned vibration-damping operationof the above mentioned shockabsorber and when part of the pressurizedgas in the chamber D invades into the interior of cylinder 1, theentrained high pressure gaseous medium may accumulate at the uppermostpart of the chamber A."

With increase of the gas accumulation thereat, it will be conveyedthrough fine gas existing between rod 3 and rod guide member 6 into thering space 7 and is accumulated therein. When considered this effect,the sealing packings 5 must have the gas leakagepreventing function, inplace of the similar action relative to the pressurized oil. As iscommonly known, a seal against a gaseous medium is highly difficultrelative to that against oil and it has been frequently concluded amongthose skilled in the art that an effective seal against a high gaspressure such as 30 40 kgs/sq. cm or so in practice substantiallyimpossible. The provision of the said communication tube 18 will servefor returningly conveying the accumulated high pressure gaseous mediumat the uppermost part of the chamber A or within the ring space 7 intothe high pressure gas chamber D formed within the interior space of thehollow rod part 3a of said piston rod 3. In this way, any escapement orleakage of the gaseous medium from the absorber system towards outsideand through the selaing means provided at the top and open end of thecylinder can be perfectly and amazingly prevented according to thisinvention which means a remarkable progress in the art. Thus, thedamping performance is highly stabilized.

Since the communication tube per se has an effective vibration dampingmeans by establishing a restricted fluid communication between the oilchamber A and the oil chamber C, oil passage 11; 14, valve 12; 15 andsprings 13; 16 and the like which establish and constitute dampingforce-generating means can be dispensed with when occasion may so desireto a rather surprising manner. This means also a further progress in theshock-absorber art.

In the modified embodiment shown in FIG. 3 from that shown in FIG. 1,the difference resides substantially in the arrangement of thecommunication tube, now denoted with 118. Other constituents haverespective same or similar design and function so that they have beendenoted with respective same reference numerals and symbols to thoseemployed in the foregoing first embodiment.

In this modification, the communication tube 118 is arranged to residesubstantially within the chamber A and its upper end 118!) passesthrough the material of the ring flange l7 acting as stop means for thepiston-rod assembly 2; 3 and opens at the upper surface 17a as shown. Onthe other hand, the lower end 1186' of said communication tube 118protrudes from the chamber A laterally through the lower end of hollowrod part 3a and the upper end of piston 2 into the central oil chamberC. A still further difference resides in the provision of a mechanicalsuspension spring 25 which is held under precompression between a springmount 26 attached fixedly at the top closed end of the hollow rod part3a, and a lower spring mount 27 which is rigidly attached to the lowerend of said cylinder 1. By reason of the said upper spring mount 26acting as a part of the foregoing one shown at 19 in FIG. 1, theremaining part of the cover shown at 119 is made of a resilient materialsuch as rubber in place of the rigid metal as was employed in theforegoing first embodiment. By the provision of this suspension spring25, the allocated weight of vehicle chassis to the present suspensionstrut can be correspondingly reduced. The operation will beself-explanatory from the foregoing without further detailed analysis ofthe present embodiment. The bore of said communication tube 118 is shownin FIG. 3 at 118a.

In a further modification shown in FIG. 4, the main difference from theforegoing resides substantially in the design and arrangement of thecommunication tube means.

In the present modification, a tubular member 218 is providedconcentrically within the interior space of the hollow rod part 30, aring-shaped space 218a formed between the member 218 and the hollow rodpart 3a and passage opening means 218bare provided at the upper end ofthe gap space 218a through the wall of the hollow rod part forestablishing fluid communication between the chamber A and the uppermostend of the latter being closed by a sealing means 218d positionedbetween the parts 3a and 218. This sealing means 218d defines theuppermost extremity of the gap space 218a and prevents the high pressuregas prevailing in the chamber D from invading into the gap space 218a.At least a passage opening 2180 is formed through the lower part of thewall of said tubular means 218 for establishing fluid communicationbetween said gap space 218a with the oil chamber C which is now formedat the lower part of the said tubular member 218. The lowermostextremity of said gap space 218a is defined by the piston 2.

In the present embodiment, the lower spring mount 27 is positioned at anintermediate point between the both end extremities of the cylinder 1,and in place of the lower end thereof in the case of the firstmodification shown in FIG. 3, on account of shorterdesign of thesuspension spring 25.

The upper spring mount 26 mounts a ball bearing unit 109 which comprisesstationary lower race 29, a rotatable upper race 28 and aplurality ofbearing balls 30 rollably mounted therebetween.

By the provision of the ball bearing unit 109, a fitting means 31 forattaching the suspension strut shown in FIG. 4 to the vehicle chassis,not shown, can be rotatable relative to the strut for avoiding thelatter from being applied an excessive turning force.

As shown, the lower end of the cylinder 1 is rigidly connected with aconventional axle-mounting member shown at 32. The upper half of theinterior space of said tube member 218 constitutes a small gas spacewhich is practically a part of the gas chamber D.

The liquid communication between the chambers A and C" is carried outthrough lateral passage means 218b, .gap space 218a and passage openingmeans 2180. The gas returning job is performed through these means.

The overall operation of the present strut is similar to that asdescribed in connection with FIG. 3.

A still further modified embodiment is shown in FIG. 5.

In the present modification, a damping valve assembly comprisinga checkvalve 312, a valve spring 313, and a limited flow passage 3180 which aresimilar to those denoted in FIG. 1 by such numerals 12, 13 and 1 1 isprovided at the lower endof communication tube 18 in place of the formerposition within the material of piston 2. Partially, otherliquid-damping and gas return operations are similar to those describedin connection with FIG. 1 so that no further analysis would be necessaryfor full understanding of the present modification. g t

It should be noted that any one feature of one embodiment can beutilized in any other embodiment, so far as no conflict is invited bysuch further design alteration.

The salient advantages with use of any of the foregoing embodiments areas follows:

1. By the employment of larger and hollow piston rod, the mechanismaccording to this invention represents a more rigidmechanism.

2. Since high pressure air or gas is sealed-in within the interiorhollow space, the damping performance or characteristics are made highlystable.

3. By the employment of the single tube mode, the overall structure israther economic in manufacture and it has an efficient heat-dissipatingperformance.

4. Leakage of the sealed-in gas from inside to outside of the mechanismcan be positively prevented.

5. Provision of the valve means will assure to modify and adjust the W-Scurve as desired and in a highly simplified manner.

A still further modification from'the first embodiment shown in FIG. 1is illustrated in FIG. 6. Substantial parts of this embodiment aresimilar to those and denoted with respective same reference numerals andsymbols as before.

At a slightly higher level than that of the ring flange I 17, there isprovided a check valve unit 418 which is fixedly mountedin the wall ofthe hollow piston rod part 3a and directs laterally and inwardly. Thecheck valve unit 418 is formed with a pair of fluid passage openings419a and 41% aligned in line with each other and a valve chamber 419kept in fluid communication therewith. The passage opening 419a isnormally closed from inside by a valve disc 420 which is resilientlyurged in its closing direction by a valve spring 422. Valve disc 420 andvalve spring 422 is contained in the valve chamber 419. Valve disc 420is fitted fixedly with a sealing ring 421 for assuring a tightly closedvalve position relative to the inlet opening 419a. It will thus be seenfrom the foregoing that this check valve unit 418 allows only aunidirectional oil flow in the direction from the chamber A towards theinterior space of the hollow piston rod part 3a. In this modifiedembodiment, the communication tube 18, 118 or 218 showing in theforegoing embodiments have been dispensed with.

It will be seen from the foregoing that when the vibration dampingmechanism is expanded under the influence of chassis vibration, thesuddenly and substantially increased oil pressure in the chamber A willescape therefrom through now opened check valve unit 418 into theinterior space of hollow rod 3a. During the flow through the reducedfluid passage, damping force will be generated at the unit 418 whichacts thus as a damping force-generating means as before.

Upon arrival of the piston 2 at its uppermost, where the inlet opening419a is brought into fluid communication with the upper part of thechamber A or even with the gas accumulating ring space 7, occasionallyaccumulated gas will be discharged through the unit 418 into the gaschamber D.

A still further modified embodiment shown in FIG. 7 is a combination ofthe first modification shown in FIG. 3 with the fourth modificationshown in FIG. 6, wherein, however, the communication tube 118 has beenreplaced by a check valve unit 418. Therefore, the structure andoperation of the present modification '19 could be fully understood byreference to FIGS. 3 and 6 and their related disclosure.

A further modified embodiment is shown in FIG. 8. This is a combinationof the second modification shown in FIG. 4 with the fourth modified,wherein, however, the communication tube 218 and its related severalparts have been replaced by the check valve unit 418. Thus, thestructure and operation of the present embodiment can be easilyunderstood by reference to the foregoing and without further detailedanalysis.

The embodiments of the invention in which an exclusive property orprivilege is claimed are as follows:

1. A vibration damper mechanism comprising a cylinder having apredetermined quantity of hydraulic fluid sealed therein, a pistonslidably mounted in the interior of said cylinder for dividing saidcylinder into first and second variable volume chambers, a hollow pistonrod having an open end secured to said piston and passing outwardly fromsaid cylinder through said first chamber, guide means for guiding saidrod in sealed sliding engagement with an aperture in one end of saidcylinder, the other end of said piston rod being closed to define ahydraulic fluid receiving chamber ad- I jacent said piston and gaschamber adjacent said other end, apertures extending through said pistonto provide permanent communication between said first and secondchambers, a fluid flow limiting conduit means secured to said hollowpiston rod and having an inlet end and an outlet end, said inlet endbeingdisposed in communication with said first chamber adjacent said gaschamber and said guide means at the position of maximum expansion ofsaid piston rod and cylinder and said outlet end being disposed incommunication with the fluid receiving chamber in said hollow pistonrod, one-way valve means extending through said piston to permit fluidflow directly from the fluid chamber'within said hollow piston rod tosaid second chamber and oneway valve means connected to the outlet endof said conduit means to permit fluid flow directly from said firstchamber to said fluid chamber within said hollow piston rod.

1. A vibration damper mechanism comprising a cylinder having apredetermined quantity of hydraulic fluid sealed therein, a pistonslidably mounted in the interior of said cylinder for dividing saidcylinder into first and second variable volume chambers, a hollow pistonrod having an open end secured to said piston and passing outwardly fromsaid cylinder through said first chamber, guide means for guiding saidrod in sealed sliding engagement with an aperture in one end of saidcylinder, the othEr end of said piston rod being closed to define ahydraulic fluid receiving chamber adjacent said piston and gas chamberadjacent said other end, apertures extending through said piston toprovide permanent communication between said first and second chambers,a fluid flow limiting conduit means secured to said hollow piston rodand having an inlet end and an outlet end, said inlet end being disposedin communication with said first chamber adjacent said gas chamber andsaid guide means at the position of maximum expansion of said piston rodand cylinder and said outlet end being disposed in communication withthe fluid receiving chamber in said hollow piston rod, one-way valvemeans extending through said piston to permit fluid flow directly fromthe fluid chamber within said hollow piston rod to said second chamberand one-way valve means connected to the outlet end of said conduitmeans to permit fluid flow directly from said first chamber to saidfluid chamber within said hollow piston rod.